The rapidly increasing missile threat to surface vessels has resulted in a critical need for improved ECM antennas. Specifically, existing missile threats to surface ships has created a requirement that ECM increase radiated power and simultaneously counter threat signals which are separated in azimuth. Existing ECM antennas comprised of semi-omni antennas cannot radiate the effective powers desired when fed with existing amplifiers. Other ECM antennas are single beam directed antennas which require an operator to steer the beam to a threat sector. Multiple beam antennas have been developed but weight restrictions for small ships limit their utility. Also, millisecond beam switching time limits the multiple target response to a prediction gating program for known threat signals. Response to multiple threats of unknown signals is accommodated by feeding beams in parallel, thereby reducing the effective radiated power. Phased array technology offers the advantages of electronically scanned, high gain beams but the resultant narrow beam with its associated high effective power is extremely sensitive to directional error. Although milliradian beam control is straightforward, the absolute alignment of the transmit beam axis with a bearing axis determined by an independent measurement of a single pulse is subject to error. This error severly degrades the effective radiated power of a pencil beam at the target location thereby imposing a high technical risk for such an approach.
Copending patent application Ser. No. 329,262 filed Jan. 15, 1973 in the name of the present inventor discloses an ECM, multiple-target, retro-directive antenna (MTRA) which overcomes the above disadvantages. A critical element in the MTRA is the beam switching processor, which must select and switch a medium-power transmit signal within 100 nanoseconds of target signal arrival.